The human pathogen Vibrio cholerae, the causative agent of the disease cholera, regulates virulence factor production, biofilm formation, competence, and other important processes through quorum sensing (QS), a cell-cell communication mechanism that relies on the production, detection, and response to chemical signal molecules called autoinducers. QS allows bacteria to coordinate population-wide gene expression and function as coordinated groups. In addition to the two canonical QS signaling pathways, we discovered that two additional chemical sensory receptors integrate into the central QS circuit of V. cholerae. Importantly, we found that disruption of these four sensory pathways altogether renders V. cholerae unable to colonize animal hosts. Our data also suggest that these two newly identified receptors detect certain unidentified extracellular molecules different from the two known autoinducers, CAI-1 and AI-2. In Aim 1, we will identify and characterize these two new signal molecules. We will also determine the biosynthetic pathways for these signals. In Aim 2, we will define the signal detection mechanisms for these two new receptors. In Aim 3, we will determine the contribution from each individual QS receptor in virulence gene expression in vivo. Together, our work will not only define the role of QS in V. cholerae pathogenesis, it will also illustrate how integration of multiple signals results in a coherent response in a bacterial cell-cell communication process. It is now well established that QS is employed by many bacterial species to regulate both harmful and beneficial traits. A long standing goal in the field is to develop pro-QS and/or anti-QS molecules to manipulate bacterial group behaviors. Our hope is to harness the knowledge on QS to enable the design of interference strategies that can be translated into new therapies to combat infectious diseases.